As illustrated in FIG. 6, the steering apparatus of an automobile is constructed such that it applies a steering angle to the front wheels by transmitting the rotation of a steering wheel 1 to an input shaft 3 of a steering gear unit 2, and pushing or pulling a pair of left and right tie rods 4 as the input shaft 3 rotates. The steering wheel 1 is supported by and fastened to the rear end section of a steering shaft 5, and with the steering shaft 5 passed in the axial direction through a cylindrical shaped steering column 6, the steering shaft 5 is supported by this steering column 6 such that it can rotate freely. The front end section of the steering shaft 5 is connected to the rear end section of an intermediate shaft 8 via a universal joint 7, and the front end section of the intermediate shaft 8 is connected to the input shaft 3 via a separate universal joint 9. The intermediate shaft 8 is constructed such that it is capable of transmitting torque, and such that its entire length can be contracted by an impact load. During a collision accident, regardless of backward displacement of the steering gear unit 2, due to contraction of the intermediate shaft 8, the steering wheel 1 is prevented from displacing toward the rear with the steering shaft 5 and thus from being pressed up against the body of the driver.
During a collision accident, it is required for this kind of steering wheel apparatus for an automobile to have construction that causes the steering wheel to displace in the forward direction as it absorbs impact energy so as to protect the driver. In other words, during a collision accident, after a primary collision of an automobile with another automobile, a secondary collision occurs in which the body of the driver hits the steering wheel 1. Technology has been conventionally employed, as disclosed in Patent Literatures 1 to 3, in which the impact applied to the body of the driver during this secondary collision is lessened by supporting the steering column 6 that supports the steering wheel 1 with respect to the vehicle body so that the steering column 6 drops away toward the front due to the impact load of this secondary collision, and by providing an energy absorbing member, which absorbs an impact load by deforming plastically, between a portion that displaces in the forward direction together with the steering column 6 and the vehicle body.
Patent Literature 4 discloses construction in which an electric power steering apparatus is installed on the front end section of the steering column, and where this steering column and a housing of this electric power steering apparatus are supported independently of each other by a portion that is fastened to the vehicle body such that they are capable of dropping away to the front due to an impact load. FIG. 7 and FIG. 8 illustrate an example of this kind of conventional construction in which the steering column and housing are supported independently of each other by the vehicle body.
A housing 10 that houses component parts such as a reduction gear of the electric power steering apparatus is fastened to the front end section of the steering column 6a. A steering shaft 5a is supported on the inside of the steering column 6a such that the steering shaft 5a can only rotate freely, and the steering wheel 1 (see FIG. 6) is fastened to a portion of the rear end section of the steering shaft 5a that protrudes from the opening on the rear end of the steering column 6a. The steering column 6a and housing 10 are supported by a bracket 11 on the vehicle side, which corresponds to the portion fastened to the vehicle body (see FIG. 4 and FIG. 5) such that they are capable of dropping away toward the front due to an impact load in the forward direction.
In order for this, a bracket 12 on the column side that is supported in the middle section of the steering column 6a, and a bracket 13 on the housing side that is supported by the housing 10 are supported by the vehicle body so that both of these drop away to the front due to an impact load in the forward direction. These brackets 12, 13 both are provided with installation plate sections 14a, 14b at one or two locations respectively, and cut out sections 15a, 15b are formed in this installation plate sections 14a, 14b with opened at the rear end edge of these sections 14a, 14b. In a state covering these cut out sections 15a, 15b, sliding plates 16a, 16b are attached to portions near both the left and right ends of these brackets 12, 13.
These sliding plates 16a, 16b are each formed by bending a thin metal plate such as carbon steel plate or stainless steel plate that is covered on the surface with a layer of synthetic resin such as polyimide resin (nylon) or polytetrafluoroethylene resin into a U shape, such that a connecting plate section connects the rear end edges of top and bottom plate sections. A through hole for inserting a bolt or stud is formed in portions of the top and bottom plate sections that are aligned with each other. With the sliding plates 16a, 16b mounted on the installation plate sections 14a, 14b, these through holes are aligned with the cut out sections 15a, 15b that are formed in the installation plate sections 14a, 14b. With regard to the sliding plate 16b which is mounted on the installation plate section 14b of the bracket 13 on the housing side, a restraining piece that is formed by bending a tab which is formed on the front end edge of the top plate of the sliding plate 16b downward or by bending a tab which is formed on the front end edge of the bottom plate of the sliding plate 16b upward, is engaged with the front end edge of the installation plate section 14b, such that the sliding plate 16b is prevented from accidentally dropping away from the installation plate section 14b before the installation to the bracket 11 on the vehicle side.
These brackets 12, 13 are supported by the bracket 11 on the vehicle side by inserting a bolt or stud through the cut out sections 15a, 15b in the installation plate sections 14a, 14b and the through holes 16a, 16b in the sliding plates 16a, 16b and screwing the bolts into the nuts and tightening. During a secondary collision, the bolt or stud comes out from the cut out sections 15a, 15b together with the sliding plates 16a, 16b, which allows the steering column 6a and housing 10 to displace in the forward direction together with the brackets 11, 12 and steering wheel 1.
In the case of the example in the figures, an energy absorbing member 20 as illustrated in FIG. 9 is located between the bolt or stud and the bracket 12 on the column side. As the bracket 12 on the column side displaces in the forward direction, this energy absorbing member 20 plastically deforms, which absorbs the impact energy that is transmitted from the steering wheel 1 to the bracket 12 on the column side via the steering shaft 5b and steering column 6a. The energy absorbing member 20 is basically the same as that disclosed in Patent Literature 1, which is formed by bending a plastically deformable metal plate such as mild steel plate, and comprises a base plate section 21 and a plastically deforming section 22. A circular hole 23 is formed in the center section of the base plate section 21 for inserting the bolt or stud. Moreover, two locations on both end sections in the width direction of the rear end edge of the base plate section 21 are bent upward to form restraining pieces 24, and the front surfaces of these restraining pieces 24 engage with the rear end edge of the sliding plate 16a that is mounted on the installation plate section 14a of the bracket 12 on the column side. These restraining pieces 24 are provided for positioning the base plate section 21 with respect to the sliding plate 16a. Furthermore, the plastically deforming sections 22 are formed by bending back the middle section of the band shaped plate section that extends forward from the center section of the front end edge of the base plate section 21 downward and toward the rear 180° into a U shape.
The base plate sections 21 of the energy absorbing members 20 having this kind of construction are supported by bolts or studs, and are connected to the vehicle body in a state where displacement in the forward direction is prevented. The tip end edges of the plastically deforming sections 22 engage with the bracket 12 on the column side where the installation plate sections 14a are located. Anchor plate sections 25 for coming in contact with the tip end edges of the plastically deforming sections 22 are formed by bending in a portion situated below the installation plate sections 14a on both the left and right sides of the bracket 12 on the column side. The anchor plate sections 25 is formed by bending the rear end section of the bottom plate section located on the lower portion of the installation plate section 14a upward, and the plastically deforming section 22 of the energy absorbing member 20 is arranged in a space between the bottom surface of the installation plate section 14a and the top surface of the bottom plate section.
During a secondary collision, the bolts or studs come out from the cut out sections 15a together with the sliding plates 16a and the base plate sections 21 of the energy absorbing members 20, which allows the bracket 12 on the column side to displace in the forward direction. The steering column 6a also displaces in the forward direction together with the bracket 12 on the column side. When this happens, the bracket 13 on the housing side also drops away from the vehicle, which allows this bracket 13 on the housing side to displace in the forward direction. As the bracket 12 on the column side displaces in the forward direction, the plastically deforming sections 22 of the energy absorbing members 20 plastically deform from the state illustrated in FIG. 8 to the state illustrated in FIG. 10 in a direction that causes the bent back section of that is formed in the middle section of the band shaped plate section to move toward the tip end side of this band shaped plate section. The plastic deformation absorbs the impact energy that is transmitted from the body of the driver to the bracket 12 on the column side by way of the steering shaft 5a and the steering column 6, which lessens the impact applied to the body of the driver.
In the example illustrated in the figure, a tilting mechanism is installed for adjusting the vertical position of the steering wheel 1. In order for this, the bracket 13 on the housing side is formed in a gate like shape and is provided with a pair of left and right support plate sections 17 vertically extending from both the left and right end sections thereof, and the bottom end sections of the left and right support plate sections 17 are supported by the housing 10 by a pair of concentric left and right pivot sections 18 such that pivoting is possible. The steering column 6a is supported by the bracket 12 on the column side so that it can raise and lower along long holes that are formed in a partial arc shape around these pivot sections 18. When adjusting the vertical position of the steering wheel 1, a tilt lever 19 is rotated downward, and with the force for supporting the steering column by the bracket 12 on the column side lowered or eliminated, the steering column 6a is pivoted around the pivot sections 18. Then, with the steering wheel 1 moved to a desired position, the tilt lever 19 is rotated upward, and the force for supporting the steering column 6a by the column bracket 12 is restored.
In the case of the construction illustrated in FIG. 7 and FIG. 8, in addition to the electric motor 26 being fastened to and supported by the housing 10 that is fastened to the front end section of the steering column 6a, many parts such as a torque sensor are housed inside the housing in addition to the reduction gear, to form an electric power steering apparatus 27. This electric power steering apparatus 27 is heavy, so by providing a bracket 13 on the housing side, this electric power steering apparatus 27 is supported by the bracket 11 on the vehicle side separately from the steering column 6a. Incidentally, as a secondary collision occurs, during the process of the housing 10 displacing in the forward direction together with this steering column 6a, after the force for supporting the housing 10 by the bracket 11 on the vehicle side is lost, the rear section of this steering column 6a easily displaces upward. The reason for the rear section of this steering column 6a easily displacing in the upward direction when a secondary collision occurs is because of the following two forces (1) and (2).
(1) In the case of an actual steering apparatus, the steering column 6a is located in an inclined state in a direction upward going toward the rear. During a secondary collision, an impact load is applied to the steering wheel 1 in nearly the forward direction, so in addition to the force component in the forward direction along the center axis of the steering column 6a, a force component is applied in the upward direction, in a direction orthogonal to the center axis.
(2) The heavy electric power steering apparatus 27 that is supported by the front end section of the steering column 6a works as a force that causes the front end section of the steering column 6a to lower. On the other hand, in this state, by the installation plate sections 14a being supported by the energy absorbing members 20, this steering column 6a is in a state of being able to pivot around the bracket 12 on the column side. Therefore, the weight of the electric power steering apparatus 27 works as a force causing the rear end section of the steering column 6a to displace upward.
As illustrated in FIG. 10, when the force for supporting the bracket 13 on the housing side by the bracket 11 on the vehicle side is lost as a secondary collision occurs, the steering column 6a becomes tilted more than the original angle of inclination due to the forces of (1) an (2) above. In other words, the rear end section of the steering column 6a displaces upward more than the original position, and the front end section similarly displaces downward. On the other hand, during a secondary collision, displacement in the forward direction of the steering column 6a is performed as the plurality of locations of friction fit are caused to slide, and the energy absorbing members 20 are caused to plastically deform. The sliding of these areas of friction fit, and the plastic deformation of the energy absorbing members 20 are designed to be performed effectively when the steering column 6a displaces in the axial direction. In other words, as illustrated in FIG. 10, displacement of the steering column in the forward direction as is in an inclined state is disadvantageous from the aspect of completely protecting the driver. Moreover, this is also disadvantageous from the aspect of the difficulty of design for properly maintaining a positional relationship between an airbag that inflates at the rear of the steering wheel 1 and the body of the driver.